This invention relates to a discharge machining apparatus and, particularly, to means for spraying machining liquid to a machining portion thereof.
FIG. 6 shows schematically an example of a conventional discharge machining apparatus and FIG. 7 is an enlarged cross section of a machining portion thereof showing a relation between a workpiece and an electrode in the machining portion. In FIG. 6, the conventional discharge machining apparatus includes a machining tank 1, a machining table 3 disposed on a bottom of the tank 1, a machining electrode 4 and a pump 6 for supplying machining liquid 5 through a pressure regulating valve 7 to the machining electrode 4. A pressure meter 8 is associated with the pressure regulating valve 7. A workpiece 2 is fixedly disposed on the machining table 3.
The machining electrode 4 has a central hollow portion 4a as shown in FIG. 7.
In the conventional discharge machining apparatus constructed as mentioned above, machining liquid 5 supplied under pressure by the supply pump 6 is supplied to the hollow portion 4a of the electrode 4 at a pressure set by the valve 7 and sprayed from an end of the electrode 4.
Material particles 2a sputtered from the workpiece 2 due to discharge current resulting from pulse voltage applied across the workpiece 2 and the electrode 4 are conveyed, with vaporized high temperature machining liquid 5, along an outer periphery of the electrode 4 upwardly and are discharged as illustrated in FIG. 7.
In the conventional discharge machining apparatus applied to, for example, a machining of a through-hole in a workpiece, when a bottom of the workpiece 2 is partially opened by the electrode 4 whose end is approaching an end position of the machining during the machining of the through-hole in the workpiece 2 as shown in FIG. 8, machining liquid 5 may be discharged through this partial opening. Therefore, the pressure of machining liquid 5 which is regulated by the valve 7 is lowered, so that material particles 2a to be discharged externally along the outer periphery of the electrode 4 are accumulated in between the workpiece 2 and the electrode 4. Since a machining speed is lowered by this accumulation of material particles 2a, it is necessary to stop the machining and remove them manually, resulting in difficulties in an automated machining operation.